The present invention relates to a method for setting dyes on fabrics in general, by the two-step process, as well as a system specifically designed for carrying out this method.
As is known, the so-called two-step process for setting reactive dyes on cotton or viscose comprises a first step, in which on a textile support there is printed and dryed a semi-dense mixture, comprising a dye and a thickening agent.
The second step of the process consists of causing the fabric to pass, after the printing and drying operation, through an alkali bath with an immediately subsequent vaporizing by using slightly super-heated steam, for a period of time which can vary from 12 to 15 seconds.
Between the alkali bath and vaporizer a pre-heating device is usually included, for example, of the infrared ray type.
This process is broadly used mainly for cotton or viscose fabrics, since it provides the possibility of printing and vaporizing the fabric in different days, and allows to obtain an optimum setting of the dyes, since the vaporizing operation is substantially of a wet-on-wet type.
Moreover, no polluting additional product is used, such as urea or accelerating substances, and the method involves a low consume of power for the vaporization, together with a small cost for the dyes, which is much smaller than that required for a single-step setting process.
In order to carry out the vaporization, there is at present used a vaporizer, comprising a tower or column, inside which there are held 8-12 meters of fabric.
In the column, the fabric is entrained to vertically rise, as controlled by a driven cylinder, arranged at the top of the column, and then the fabric is caused to downwardly move and exit the processing column.
The steam which is present inside the column or processing chamber has conventionally a temperature of 130.degree. C., in order to assure a good setting of the dye.
The use of such a column derives from the fact that, during the processing operations, it is necessary that the printed side of the fabric does not rub on the cylinder since such a rubbing would damage the printed material.
This is a great limitation for the use of the above mentioned process, since the processed fabric will have, for each processing cycle, a length of only ten meters, since it would be not possible to make columns having excessively great heights.
Moreover, the use of a column or tower apparatus prevents the two step system from being applyed to knitted fabrics which would be susceptible to roll up on the fabric selvage during the up and down displacements through the vaporizing column.